I walked with Roberto Navarrete into the national stadium in Santiago, Chile. With the southern winter's wind skating down from the Andes, it was empty and ghostly. Little had changed, he said: the chicken wire, the broken seats, the tunnel to the changing rooms from which the screams echoed. We stopped at a large number 28. "This is where I was, facing the scoreboard. This is where I was called to be tortured."

Thousands of "the detained and the disappeared" were imprisoned in the stadium following the Washington-backed coup by General Pinochet against the democracy of Salvador Allende on September 11 1973. For the majority people of Latin America, the abandonados, the infamy and historical lesson of the first "9/11" have never been forgotten. "In the Allende years, we had a hope the human spirit would triumph," said Roberto. "But in Latin America those believing they are born to rule behave with such brutality to defend their rights, their property, their hold over society that they approach true fascism. People who are well-dressed, whose houses are full of food, bang pots in the streets in protest as though they don't have anything. This is what we had in Chile 36 years ago. This is what we see in Venezuela today. It is as if Chávez is Allende. It is so evocative for me."

In making my film The War on Democracy, I sought the help of Chileans like Roberto and his family, and Sara de Witt, who courageously returned with me to the torture chambers at Villa Grimaldi, which she somehow survived. Together with other Latin Americans who knew the tyrannies, they bear witness to the pattern and meaning of the propaganda and lies now aimed at undermining another epic bid to renew both democracy and freedom on the continent.

The disinformation that helped destroy Allende and give rise to Pinochet's horrors worked the same in Nicaragua, where the Sandinistas had the temerity to implement modest, popular reforms. In both countries, the CIA funded the leading opposition media, although they need not have bothered. In Nicaragua, the fake martyrdom of La Prensa became a cause for North America's leading liberal journalists, who seriously debated whether a poverty-stricken country of 3 million peasants posed a "threat" to the United States. Ronald Reagan agreed and declared a state of emergency to combat the monster at the gates. In Britain, whose Thatcher government "absolutely endorsed" US policy, the standard censorship by omission applied. In examining 500 articles that dealt with Nicaragua in the early 1980s, the historian Mark Curtis found an almost universal suppression of the achievements of the Sandinista government - "remarkable by any standards" - in favour of the falsehood of "the threat of a communist takeover".

The similarities in the campaign against the phenomenal rise of popular democratic movements today are striking. Aimed principally at Venezuela, especially Chávez, the virulence of the attacks suggests that something exciting is taking place; and it is. Thousands of poor Venezuelans are seeing a doctor for the first time in their lives, having their children immunised and drinking clean water. New universities have opened their doors to the poor, breaking the privilege of competitive institutions effectively controlled by a "middle class" in a country where there is no middle. In barrio La Línea, Beatrice Balazo told me her children were the first generation of the poor to attend a full day's school. "I have seen their confidence blossom like flowers," she said. One night in barrio La Vega, in a bare room beneath a single lightbulb, I watched Mavis Mendez, aged 94, learn to write her own name for the first time.

More than 25,000 communal councils have been set up in parallel to the old, corrupt local bureaucracies. Many are spectacles of raw grassroots democracy. Spokespeople are elected, yet all decisions, ideas and spending have to be approved by a community assembly. In towns long controlled by oligarchs and their servile media, this explosion of popular power has begun to change lives in the way Beatrice described.

It is this new confidence of Venezuela's "invisible people" that has so inflamed those who live in suburbs called country club. Behind their walls and dogs, they remind me of white South Africans. Venezuela's wild west media is mostly theirs; 80% of broadcasting and almost all the 118 newspaper companies are privately owned. Until recently one television shock jock liked to call Chávez, who is mixed race, a "monkey". Front pages depict the president as Hitler, or as Stalin (the connection being that both like babies). Among broadcasters crying censorship loudest are those bankrolled by the National Endowment for Democracy, the CIA in spirit if not name. "We had a deadly weapon, the media," said an admiral who was one of the coup plotters in 2002. The TV station, RCTV, never prosecuted for its part in the attempt to overthrow the elected government, lost only its terrestrial licence and is still broadcasting on satellite and cable.

Yet, as in Nicaragua, the "treatment" of RCTV is a cause celebre for those in Britain and the US affronted by the sheer audacity and popularity of Chávez, whom they smear as "power crazed" and a "tyrant". That he is the authentic product of a popular awakening is suppressed. Even the description of him as a "radical socialist", usually in the pejorative, wilfully ignores the fact that he is a nationalist and social democrat, a label many in Britain's Labour party were once proud to wear.

In Washington, the old Iran-Contra death squad gang, back in power under Bush, fear the economic bridges Chávez is building in the region, such as the use of Venezuela's oil revenue to end IMF slavery. That he maintains a neoliberal economy, described by the American Banker as "the envy of the banking world" is seldom raised as valid criticism of his limited reforms. These days, of course, any true reforms are exotic. And as liberal elites under Blair and Bush fail to defend their own basic liberties, they watch the very concept of democracy as a liberal preserve challenged on a continent about which Richard Nixon once said "people don't give a shit". However much they play the man, Chávez, their arrogance cannot accept that the seed of Rousseau's idea of direct popular sovereignty may have been planted among the poorest, yet again, and "the hope of the human spirit", of which Roberto spoke in the stadium, has returned.

· The War on Democracy, directed by Christopher Martin and John Pilger, will be shown on ITV on Monday at 11pm.